Published online by Cambridge University Press: 01 March 2011
This chapter includes borderline to low-grade malignant vascular tumors (hemangioendotheliomas) and malignant vascular tumors (angiosarcoma and Kaposi's sarcoma).
Hemangioendothelioma is the designation for a group of borderline or outright malignant vascular tumors. They are capable of aggressive local growth, recurrence, or both, and some, especially epithelioid hemangioendothelioma, can also metastasize.
Angiosarcomas (AS) are malignant endothelial neoplasms. They are very rare compared with hemangiomas and comprise <1% of all vascular tumors and only 1% to 2% of all sarcomas. ASs are essentially composed of malignant endothelial cells representing endothelial cell neoplasms. They include rare low-grade variants but most are the high-grade variety. The features that aid in recognition of an angiosarcoma are disorganized and anastomosing vascular channels, permeative growth versus lobulation of the vascular units, and multilayered, atypical endothelia, often with solid areas, and a general lack of pericytes of the vessel wall. Lymphangiosarcomas are not recognized separately. ASs are frequently multifocal, making it sometimes difficult to determine the primary site. Because of this multifocal tendency, angiosarcomas are excluded from sarcoma staging systems.
Radiation and environmental carcinogens play a causal role, the latter especially in hepatic ASs. By their location, the endothelial cells are directly exposed to circulating carcinogens. The genetic mechanisms related to the pathogenesis of AS are much less understood than those for many other sarcomas, however.
Kaposi's sarcoma is etiologically related to human herpesvirus 8, which is one of the strongest connections between a virus and human mesenchymal neoplasia.
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